Method of making a glass-to-metal seal



July-17, 1951 J. A. PAsK ETAL 2,560,593

METHOD oF MAKING A GLAss-To-METAL SEAL Filed May 4, 1945 l Y l l Bras/WM5 (ff- Nec.)

77MLe /A/ M//varss ATTORNEY Patented July 17, 1951 UNITED STATES PATENT OFFRE 'I METHUD 0F MAKING A GLASS-i-'IO-MTAL v SEAL Joseph A. Pask and JohnE. Schiveree, Bloomfield,

' N. J., assignors to Westinghouse Electric Conporation, East Pittsburgh, Pa., a corporation ofiennsylvania Application May il, 1945, Serial No. 591,998 I This invention relates to sealing glass to metal, and particularly to partsformed of a nickel-cobait-iron alloy,identiiied in the Lempert et al.

. Patent No. 2,279,831, dated April 14, 1942, Where 2 Claims. (Cl. iii-81) accordance with our invention we roughen the metal, either by preoxidation, sand blasting, or chemical treatment, it being understood that sand blasting and chemical treatment may also it is designated Kovarf 5' be combined, lthe former serving as an initial The principal object of our invention, generalcleaning step, after which anenamel-like layer oi ly considered, is to seal glass to metal, avoiding a sealing glass may be applied. non-vacuum-tight joints due to over oxidation of 'I'he next or normal step of sealing a glass part the metal, as by coating the metal, which may be to a metal part simply resolves itself into sealing the nickel-cobalt-iron alloy above identied, all0 glass to vglass in accordance with the usual rules, loys of iron and nickel, tungsten, copper, nickel, during which procedure the interface conditions or the like, the surfaces of which are to be sealed, established during the glass enameling remain with a thin protective glass layer prior to the norsubstantially xed. Such glass enameling mal seal working. methods lend themselves to mass production, Another object of our invention is to prepare l5 since all roughenng treatment and fusing of glass the glass for-coating metal, prior to making the coatings are carried out in controlled, preferably desired seal, by grinding said glass to powder andl electrically-heated, ovens that can be of the con- Y suspending in a liquid, such as water or alcohol, tinuous type. All of such seals may be made uni- Y said liquid preferably containing some electroform because the humanvelementis eliminated.

lyte, such as a small proportion of lithium nitrate, 20 In connecting glass to. for example an article if alcohol is used as the liquid, as well as possibly of a nickel-oobalt-iron alloy. Such as previously containing clay or organic binder, in order to identified, the latter is desirably enameled withv provide a nlm/of unmed glass with sufficient a'glass. positively identied as Corning No- '7052. strength for handling. or other glass having approximately the same co- A still furtherobject of our invention is to pre- 25 efcent of expansion aS the allOy- Corning GiaSS pare the metal, prior to application of the glass No. '1052 is a potash-barum-borosilioate glass coating, with the surface to be coated of consold under the trade-mark Pyrex laboratory trolled roughness, as by baking in a hydrogen at- No. G-705-FN, for sealing purposes. It has a mosphere to clean, and then roughening by consoftening point at 708i5 C an annealing P01111? trolled preoxidation, sand blasting, or chemical .m at 480 C.. a strain point at 442 C..'a'00emc iel1i of treatment, whereby after the glass suspension ls expansion of 4611.5 X 10'I between 0 and 300 C.. applied, heating causes the glass particles to fuse y a working point at approximately 1115 C. and a over onthe surface. density of 2.29. The' logmof its resistivity at 350 `Other objects and advantages of the invention C. is '7.40.V Its power factor is .0026 (expressed as will become apparent as the description proceeds. 35 a decimal-not as per cent), its dielectric con- Referrng to the drawing: l stant 5.1, and its lossfactor .0133 (expressed as Fig. lis a ilow diagram showing; first, how the a decimalnot as per cent). The nickelcobaltglass is prepared;v second', how the metal is preiron alloy referred to has been developed to have pared; and third, how the glass preparation is ,l `a coefficient of expansion approximating that of applied t0 the prepared metal: o glass, such as that above identiiled, suitable for Fig.` 2 lis a graph showing typical or average 'use in making vacuum devices. It is merely' ill rates of oxidation of sheets of the nickel-cobaltlustrative of metal to which glass may be'sealedv iron alloy. previously identified, of small sizes in accordance with our invention.L Inso doing; it' which have been used, at various temperatures; is found that the adherence to the alloy, rough- Fig. 3 is an elevational view of a ring of the 45 ened by oxide, was dependent on the amount of f v"nickel-cobalt-iron alloy, previously ldentied oxide only, and not related to the temperature of' partly coated with glass in accordance with our preoxidation, except for the fact that higher invention; temperatures required shorter times for develop- Fig. 4 is a transverse sectional view on the line ment of a given oxide ooating IV-IV of Fig. 3 in the direction of the arrows; 50 Referring to the drawings, Fig. 1 is a ilow diaand l' c gram indicating that the glass is prepared by Fig. 5 is a, portion of a vacuum tube incorporatfirst making it into a iine powder.. 'Ihis glass is ing rings such as illustrated in Figs. 3 and 4; ground, preferably by ball milling in porcelain We propose glass enameling or powder glassing apparatus so that it will pass through 100 mesh as anew stepinmaking glass-to-metal seals. In 55 screen. If any other form of grinding is employed, wherein the glass comes in contact with metallic surfaces, the resulting metallic contamination should be removed.

The powdered glass so produced is suspended in a liquid which preferably contains some electrolyte. If alcohol is used, the preferred electrolyte is a small proportion, such as .003 gram of lithium nitrate per gram of glass, per 1.19 cc. of alcohol. The electrolyte helps to keep the glass from settling out too rapidly. It will, however, be understood that we do not wish to be restricted to alcohol as the suspending vehicle, as water or other liquid may be substituted. If water is used, other forms of electrolyte may be preferable as compared with lithium nitrate. It may also contain a suspending agent such as clay. gum tragacanth, starch, or the like.

' The metal to be coated, in this instance, we are considering the identified alloy as a mere example, is rst cleaned by baking in hydrogen according to the factory time-temperature schedule for the size ofthe piece. It is then roughened, as by pre-oxidation to a predetermined weight per unit surface, or by sand blasting and/or chemical treatment.

If the identified alloy is roughened by oxidation, it has been found that holding at about 900 C. for about three minutes in an electrically heated oven gives good results. However, other time-temperature conditions which give the same weight of oxide on the surface, that is about .0005 to .0007 gram per sq. cm., in accordance with the graph of Fig. 2 may be employed; such as about one minute at about 1000" C. or about fifteen minutes at about 800 C. The minimum amount of oxide for satisfactory adherence, and the desirable mouse gray color which indicates it, with the Corning No. '7052 glass which was used, is about .0004 gram per sq.`cm,; the maximum is apparently determined by the amount of oxide the glass will absorb, on the one hand, or the point at which the oxide begins to scale off, on the other.

If some other method of metal treatment is employed, such as sand blasting, this may serve 'as an initial cleaning step and be followed by chemical treatment. The latter, for the identified alloy is desirably obtained by immersion in hot concentrated hydrochloric acid for ten minutes. Microscopic examination has shown that all seals with good adherence have a rough, nely pitted, matte-like surface, and those with poor adherence have definite small fiat crystalline faces in the metal surface which appear as dark specks in a microscopic View. 'I'he latter condition is also associated with a shiny surface. Itwill, however, be understood that any treatment resulting in a roughened surface which causes satisfactory glass adherence is within the scope of our. invention. f

It is considered that a very thin oxide layer, or4 adsorbed oxygen layer, is necessaryy for the glassV to wet the metal. Consequently, even a surface with proper texture will exhibit poor adherence if A away from the metal. This indicates that the adherence of `the glass to the metal for the acid- 4 treated specimens, just as for the properly oxidized ones, was greater than the strength of the glass.

The suspension of glass is applied to the metal lsurface treated in accordance with one of the aforementioned .processes by spraying. dipping or flowing thereon. The thickness of the coating may be up to 1 mm., depending on the purpose for which the coated metal is to be used. Figs. 3 and 4 illustrate a disk il of the identified alloy which has been coated with glass I2, applied as a suspension. It will be noted that the entire relatively large flat surface of the disk is not coated,

but'that the area coated is quite large per unit length, as compared with that of a small wire. This effect may be accomplished by coating the entire surface and, after drying, brushing the undesired glass from the treated metal surface. As analternative the glass suspension may be applied by using a stencil to keep the portions of the metal which are not to be coated free from the coating material.

The metal after coating is heated in any type of furnace or by induction. This heating may be accomplished in air or a controlled atmosphere. Good results'with the'identiiled alloy have been obtained by tiring t about l000 C. for about six minutes. Even if the surface is pre-oxidized, it may be desirable to fire in a neutral atmosphere in order -to avoid additional l' whereby a vacuum tight vessel i3, such as illustrated in Fig. 5, for example, may be built up, involving alternate sectionsof glass and metal in the present instance, will be successful. The glass dissolves and penetrates the oxide layer to come in contact with the metal. If heating is insuflicient or if too much oxide is present, an actual oxide coating may exist which would be apt to cause a leak.

By practicing our method we are able to produce seals, especially those of the large or multiple typefthat are strong and vacuum tight, that require less skill on the part of the operator, and 'that previously have been practically impossible to make because of excessive oxidation during the process of assembly. Shrinkage is decreased becausev the glass-coated parts always have a controlled oxide coating or a properly roughened interface. Production is increased, since ythe need ofY excessive working by the operator of the glass-metal interface during sealing operations is eliminated. By using this invention, some operations that. have not been practicable to date, since accurate control was previously not available, as well as normal processes, will now lend themselves to controlled mass production.

Although preferred embodimentsof our invention have been disclosed, it will be understood that modications may be made within the spirit and scope of the appended claims.

l. The method of forming an envelope consisting of alternateA sections of nickel-cobaltiron alloy and glass having approximately the same coeilicient of expansion, comprising forming flat rings of said alloy, applying a preoxidiza thin layer of glass of approximately the same coefiicient of expansion, and then connecting be tween adjacent rings, sections of the glass envelope to be formed, said envelope sections abutting the glass covered surfaces of said rings and sealed thereto, leaving metal' edges projecting therefrom.

2. The method of forming an envelope comprising constructing at rings of an alloy of nickel, cobalt, and iron, oxidizing the surface of said rings, coating said rings inside the edges thereof with a layer of glass of approximately the same coeicient of expansion as that of said alloy, and then connecting between adjacent rings sections of a glass envelope to be formed, said envelope sections abutting the glass coated surfaces of said rings and sealed thereto, whereby metal edge portions project from said envelope. f

JOSEPH A. PASK. JOHN E. SCHIVEREE.

REFERENCES CITED The following references are of record in the file of this patent:

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